408 THE BRAIN 



the anterior perforated substance. It is continuous, round 

 the frontal pole, with the superior frontal gyrus, and it turns 

 round the medial orbital border on to the medial surface of 

 the hemisphere. 



Gyri Orbitales. The orbital gyri are medial, lateral, 

 anterior and posterior. The medial and lateral are con- 

 tinuous with the anterior and posterior, both anteriorly and 

 posteriorly. 



The medial orbital gyrus lies between the olfactory 

 sulcus and the medial limb of the H-shaped sulcus. The 

 anterior and the posterior orbital gyri are respectively 

 anterior and posterior to the transverse bar of the H-shaped 

 sulcus ; and the lateral gyrus is to the lateral side of the 

 lateral limb of the sulcus. 



The medial orbital gyrus is continuous with the superior 

 frontal gyrus ; the anterior orbital gyrus is in continuity with 

 the middle frontal gyrus ; and the lateral orbital gyrus, with 

 the inferior frontal gyrus; whilst at the bottom of the stem 

 of the lateral fissure the posterior orbital gyrus is separated 

 from the temporal lobe by the lower part of the insula. 



The medial surface of the frontal lobe will be examined at a later 

 period ; but the dissector should note that upon its medial surface are a 

 part of the superior frontal gyrus, a part of the gyrus cinguli and a part of 

 the paracentral lobule (Fig. 159). - 



Lobus Parietalis. The parietal lobe appears on the 

 supero-lateral and the medial surfaces of the hemisphere, 

 and its lower portion forms the upper wall of the posterior 

 horizontal ramus of the lateral fissure. The part on the 

 medial surface which forms the precuneus, and takes part in 

 the formation of the paracentral lobule and the gyrus cinguli, 

 will be examined at a later period. The inferior portion 

 partly abuts against the temporal lobe, along the superficial 

 part of the posterior ramus of the lateral fissure, but, more 

 deeply, it is in close relation with the insula, from which it 

 is separated by the circular sulcus. The dissector should 

 verify these facts by gently separating the lips of the posterior 

 ramus of the lateral fissure. 



The Supero-lateral Surface of the Parietal Lobe lies entirely 

 under cover of the parietal bone, and is bounded, above, by 

 the supero-medial border of the hemisphere ; below, by the 

 posterior ramus of the lateral fissure and by a line projected 

 horizontally backwards from the point where that fissure turns 



